Browsing by Subject "Subarctic lakes"

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  • Korkonen, Sanna; Weckström, Jan; Korhola, Atte (2020)
    The occurrence of various chrysophyte cyst morphotypes is unknown in Finland, with the exception of a few isolated lake studies. We set out to chart which cyst types are found in Finland and what their ecological preferences are, focusing on cyst-air temperature relationships that could be further utilized in reconstructing past winter/spring air temperatures and ice-free periods from sedimentary cyst assemblages. Surface sediment samples from lakes across Finland were analysed for their chrysophyte stomatocyst assemblages. Multivariate ecological techniques (e.g. canonical correspondence analysis, principal component analysis) were used to identify the environmental variables that most strongly affected the distribution of the cysts. This survey expanded the known geographical range for several cyst types. Lake water pH and ice-free periods (surrogate for air temperature) explained the statistically significant distribution and composition of the cyst assemblages studied. The results broaden our knowledge of cyst biogeography and strengthen the findings of previous studies of the environmental factors contributing to the occurrence of cysts. Highly variable and rich chrysophyte cyst assemblages in Finland are clearly associated with temperature, pH, electrical conductivity and total phosphorus, with good potential in contemporary and retrospective environmental assessment.
  • Tuomela, Nea (Helsingin yliopisto, 2022)
    Climate change causes changes in the Arctic lakes, such as shortening of the ice-covered period and changes in hydrology as well as vegetation of the drainage area around the lakes. With these shifts in the function of the ecosystems, dissolved organic matter drainage from terrestrial sources is expected to increase. Terrestrial, allochthonous DOM is more refractory, higher molecular weight organic matter, which is less available to bacterial consumption. Alterations in the DOM pool of the lake may change the bacterial community composition, which could in turn alter the lake ecosystem. Four ice-covered lakes in Kilpisjärvi region were sampled in spring 2021. Water samples were filtered and analyzed for dissolved and particulate nutrients and carbon. Coloured dissolved organic matter and fluorescent dissolved organic matter properties were defined. Bacterial community composition was determined with multiplex polymerase chain reaction and sequences analyzed with DADA2 pipeline. Principal component analysis (PCOA) was done to visualize differences between lakes, and distance-based redundancy analysis (dbRDA) was used to detect any associations between dissolved organic matter properties and bacterial community composition. The lakes had low nutrient and carbon concentrations and had mainly similar properties of dissolved organic matter. However, P3 surface water had higher nitrate and total dissolved nitrogen concentrations. Optical properties in P3 surface water, Peak T, Peak M, biological index and humification index, indicated autochthonous production and lability of organic matter. This was reflected also in bacterial community composition by higher relative abundance of Gammaproteobacteriales. Lake P3 had also higher relative abundance of Cyanobacteria, which could be the cause for labile organic matter in the site. Sites P2 and P3 had similar bacterial community compositions, which is likely due to the sites forming a lake chain and sharing the same catchment area. The sites were oligotrophic and low nutrient environments as expected in the arctic environment. One of the sites had indications of more labile organic matter, which was reflected in the bacterial community structures. In the future shorter ice-cover period may induce autochthonous production such as Cyanobacteria, which reflects in the bacterial community. Changes in the DOM properties and bacterial communities can alter the whole food chain. with A more comprehensive study on this issue could be useful way of understanding the carbon cycling and impacts of climate change to the subarctic lakes.
  • Sanchez-Hernandez, Javier; Hayden, Brian; Harrod, Chris; Kahilainen, Kimmo K. (2021)
    A mechanistic understanding of how environmental change affects trophic ecology of fish at the individual and population level remains elusive. To address this, we conducted a space-for-time approach incorporating environmental gradients (temperature, precipitation and nutrients), lake morphometry (visibility, depth and area), fish communities (richness, competition and predation), prey availability (richness and density) and feeding (population niche breadth and individual trophic specialisation) for 15 native fish taxa belonging to different thermal guilds from 35 subarctic lakes along a marked climate-productivity gradient corresponding to future climate change predictions. We revealed significant and contrasting responses from two generalist species that are abundant and widely distributed in the region. The cold-water adapted European whitefish (Coregonus lavaretus) reduced individual specialisation in warmer and more productive lakes. Conversely, the cool-water adapted Eurasian perch (Perca fluviatilis) showed increased levels of individual specialism along climate-productivity gradient. Although whitefish and perch differed in the way they consumed prey along the climate-productivity gradient, they both switched from consumption of zooplankton in cooler, less productive lakes, to macrozoobenthos in warmer, more productive lakes. Species with specialist benthic or pelagic feeding did not show significant changes in trophic ecology along the gradient. We conclude that generalist consumers, such as warmer adapted perch, have clear advantages over colder and clear-water specialised species or morphs through their capacity to undergo reciprocal benthic-pelagic switches in feeding associated with environmental change. The capacity to show trophic flexibility in warmer and more productive lakes is likely a key trait for species dominance in future communities of high latitudes under climate change.